This invention relates to jet assemblies and has particular reference to such assemblies for the spinning of cellulose filaments from a solution of cellulose in a suitable solvent.
Cellulose may be dissolved in a tertiary amine oxide, for example by the method described in U.S. Pat. No. 4,246,221, the contents of which are incorporated herein by way of reference. Once the cellulose has been dissolved in the solvent, cellulose filaments can be prepared by spinning the solution, commonly referred to as a dope, through a spinnerette into a water bath via an air gap. The cellulose solution is processed at an elevated temperature--typically about 100.degree. C. to 110.degree. C.--and is supplied in the heated condition to the spinnerette for spinning purposes.
The cellulose solution is viscous and has to be pressurised to very high pressure levels--typically 100 to 200 bar for pumping purposes. The use of such high pressures means that the jet assemblies used to spin such solutions experience (as a result of pressure drops in the dope supply system) operating pressures of 30-50 bar. Even higher pressures can be experiences by the jet assembly during start up when the dope is cooler, and hence more viscous. Thus the assemblies have to be of a substantial construction, particularly if they are large and hence the forces involved are large. The jets must in practice be capable of withstanding these forces.
When producing cellulose for use as staple fibre, it is economically essential to produce large numbers of cellulose filaments simultaneously. This inevitably means that the spinning jet assemblies have to be relatively large and, therefore, the forces exerted by the pressurised cellulose become very high. It is necessary to use jet assemblies which can withstand such high forces.